1. Field of the Invention
The present invention relates to an adjustable back-lighting structure for a keyboard, and in particular to a structure adjusting surrounding light.
2. Description of Prior Art
To generate even flat light beams, typical back-lighting modules have light guide panel and light entering area on vertical peripheral edges of the light guide panel. When illuminating elements project light into the light entering area, light bounces between an upper and lower faces of the light guide panel, and then projects from the projecting surface. However, typical back-lighting modules trend to leak light from side edges, as shown in FIG. 1, the light guide panel 1 made of plasticized material has a projecting surface 12 and a first reflecting surface 13 as the upper and lower faces, which have some refracting capability. When the light B0 enters into the light entering surface 11, partial of the light B0 refract from the projecting surface 12 and the first reflecting surface 13, and partial of the light B0 forms a reflecting beam Br. The reflecting beam Br moves forward with a small incident angle and reaches the vertical peripheral edges 14 with a small refracting angle such that the reflecting beam Br tends to refract away from the vertical peripheral edges 14. A conventional method is to place a the seal strip 15 around the vertical peripheral edges 14 to prevent the reflecting beam Br from leaking, or to provide a second reflecting surface 150 on the seal strip 15 corresponding to the surface of the vertical peripheral edges 14, to reflect the reflecting beam Br back into the light guide panel 1. However, to form the typical light guide panel 1, the surface of the vertical peripheral edges 14 is not very even, after the seal strip 15 being placed onto the vertical peripheral edges 14, a gap 140 is formed between the vertical peripheral edges 14 and the seal strip 15 which leaks the refracting beam as beam B.
Another conventional method is to apply a layer of opaque ink at four surrounding edges of the light guide panel. However, the opaque ink layer cannot block the light completely and cannot fill up the gap.